This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Diffraction data will be collected from a complex of proteins that are critical to the function of a Type IVb secretion system in Legionella pneumophila. The T4bSS is required for infectivity and bacterial replication. Legionella pneumophila infections lead to a debilitating pneumonia that can be fatal in persons with a weakened immune system. This is particularly dangerous in hospital settings, such as transplant and burn wards. The crystals contain a 1:1 complex of the interacting region of IcmR, denoted Rm, and the full IcmQ proteins. The presence of IcmR likely blocks the function of IcmQ and acts as a chaperone to prevent aggregation. Our goal in this trip is to collect a higher resolution native data set (beyond 2.8A). The all alpha helical complex is ~24 kDa and we have engineered a complex with three Seleno-methionines. We will collect a multi-wavelength MAD dataset from Se-Met derivative crystals. This will allow us to solve the structure and then design mutations to test the function of this critical complex